The invention relates to a switching amplifier having an input and an output, means being provided for inhibiting current flow in the output in such a way that the output is isolated from the input and assumes a high-impedance state. Such amplifiers may inter alia be used in sample-and hold circuits in order to isolate the input of, for example, a Miller integrator from a signal input. Such an amplifier used for this purpose is known from IBM Technical Disclosure Bulletin, Vol. 19, No. 11, April 1977, pages 4211-4212. This amplifier comprises a pnp-differential pair with signal take-off via an npn-current mirror. An isolating diode is arranged between the collector of the output transistor of this current mirror--which collector is connected to the output--and the collector of the associated pnp-transistor of the differential pair. In order to switch off the amplifier, the flow of current in the current mirror is inhibited by draining the collector currents of the transistors of the differential pair via two diodes. As a result of this, the current-mirror transistors are turned off and the diode is also turned off, so that no current flows in the output. The drawback of this amplifier is that the amplifier does not have a class-B output stage and that the output is connected to the collector of a transistor (the output transistor of the current mirror) and to the cathode of the diode, which cathode is equivalent to an emitter. The stray capacitances involved in the case of the collector have different, in particular, larger values than in the case of the diode so that the turn-off transient of the transistor is larger than the turn-off transient of the diode and, as a consequence, the two turn-off transients do not compensate for each other at the output.
If the switching amplifier is a class-B amplifier it is often necessary to equip this class-B amplifier with two output transistors of the same conductivity type in order to achieve a sufficiently high bandwith, because in most IC techniques, only transistors of one of the two conductivity types can be fabricated with satisfactory high-frequency properties. However, again this presents the problem that the output is connected both to the collector of a switched transistor and to the emitter of a switched transistor, which results in annoying switching transients at the output.